Plastic and glass containers or bottles are prevalent in a wide variety of shapes and sizes for holding many different types of materials such as detergents, chemicals, motor oil, beer, etc. These containers are glass or plastic (mono or multi layers) of polyethylene, polypropylene, polyester or vinyl along with other specialty blends for specific barrier and product resistance performance. Generally such containers are provided with a label which designates the trade name of the product and may contain other information as well. The early art which still is prevalent today employed the use of labels manufactured from paper substrates that were applied with a water based adhesive. Subsequently, dry pressure sensitive self adhesives and in mold labels manufactured from paper have been and continue to be used. The shortcomings of paper labels with regard to tearing, wrinkling, creasing and the like due to age and moisture, or due to a lack of deformability when applied to a deformable plastic substrate have been well documented in the labeling industry. Because of this and the need to produce recyclable plastic containers, over the years a great deal of effort has been expended to develop container decoration techniques and durable polymeric film substrates or face stocks which would overcome these shortcomings. Film facestocks for container decoration which have resulted from these efforts can be applied to glass and plastic containers as self adhesive pressure sensitive labels as described in the prior art. The use of self adhesive paper and film “pressure sensitive adhesive” (PSA) labels that have been preprinted and supported on a release liner is not a cost effective option because of the added cost of the release liner used to support and render processable the self adhesive face stock. The cost of this type of structure combined with the added cost of disposal of the liner does not make pressure sensitive labeling a desirable option from an economic or environmental standpoint. In addition, new capital intensive labeling equipment is required to transition from wet applied Post Mold Labels (PML) to self adhesive PSA labels plus the effect of a new process on an existing packaging line in terms of learning cure and experience. Cut PML labeling equipment typically will run to six times the speed of a PSA labeling system.
Another film face stock labeling technique that has evolved is the use of heat activated in—mold labels as described in the prior art where a preprinted plastic label with a heat activated adhesive on the back of the label is placed in the mold before the molten plastic resin is injected or blown into the mold cavity at elevated temperature and pressure which activates the adhesive and fuses the label substrate to the container in-mold. The use of film based in-mold label substrates presents a more cost effective alternative then self adhesive pressure sensitive labels in terms of substrate cost but as this technology has progressed, it has been found that productivity is impacted by the label feeding step into the mold which is performed in a complex, continuous and rapid manner which can result in large amounts of scrap material. Also, the initial capital investment required to tool up for a container specific in-mold label process for new molds and the complex electromechanical maintenance intensive feeding devices is significant. Another detriment for this process is the potential inventory carrying costs for varieties of labeled containers that come into play with predecorated containers such as in-mold for those who would choose to apply the label immediately pre or post filled.
Post mold decoration of glass and plastic containers in the current art can also be accomplished by direct screen printing on the container. Direct screen printing on the container is not a cost effective process and also presents the aforementioned inventory problems along with added cost for freight to and from a screen printer. The graphical possibilities for label copy are limited in terms of cost and quality with this technique. Commodity products can not support the cost of this labeling technique.
Another post mold technique that has been popular is the “Thermage” process. This process transfers a reverse printed image from a transfer release paper under temperature and pressure to produce decorated containers. The “Thermage” technique of transferring a reverse printed image is costly because of transfer release paper costs and presents the same disposal problems and costs with the transfer sheet as occurs with the aforementioned release liner used in conjunction with self adhesive labels.
Other techniques for labeling various plastic and glass containers with preprinted paper or film label substrates include the use of hot melt adhesives which are applied to the label substrate or container in a molten state with container and substrate subsequently married while the hot melt is molten. When the hot melt adhesive cools, it sets up and bonds the label substrate to the container.
This technology requires the use of sophisticated melting and application equipment that must be operated, cleaned and maintained at elevated temperatures. This technology works well with complete 360 degree wrap around labels but has not evolved to the point to allow consistent labeling of a die cut or square cut “patch label” with less than 360 degree wrap. Affixing a patch label to an area on a container with 100% or patterned adhesive application using hot melt adhesives has not been commercially perfected. Complete wrap around hot melt applied labels where one end of the label is affixed to the container while the other end is wrapped around the container greater than 360 degrees to form a glue lap where the trailing edge is affixed with hot melt to the leading edge of the label substrate is proven hot melt label application technology that works well for film and paper label substrates. This labeling technique does not fit for applying patch labels on individually labeled panels of containers such a rectangular oil, contoured detergent or beer containers where a neck and front label only are applied. Another drawback is the added cost for label substrate when this technique is used since more label substrate is required because of the 100% wrap around.
Lastly, and still one of the most prevalent labeling techniques is the application of paper based cut patch labels to glass and plastic containers using natural and synthetic laminating adhesives such as BL300 produced by Henkel Adhesives or OC353-20 produced by O.C. Adhesives Corp. which are known to the art. This is a safe (water based) proven technology that has grown and been employed for many years and consequently there are many existing machines that have been installed for this type of labeling technique such as from Krones, Neutraubling, Germany that run precut patch labels or Koyo, Japan which runs roll stock that is cut into a rectangular or square patch label on the labeling machine to the label size. The cut label techniques and associated adhesives work well with paper based substrates applied to glass or plastic containers because the wet adhesive wicks (absorbs) into the paper substrate from the applicator roll, pad or pallet which breathes and allows the moisture from the water carrier to be absorbed by and dry thru the paper base.
This technique obviously will not work with non-porous polymeric label substrates as the adhesive cannot dry thru (wick into) the polymeric substrate. The adhesive and polymeric label substrate must be chosen to have initial tack and adhesive transfer to the label. Typically, wet applied cut label machines work where glued pallets remove the label out of the label holding magazine while simultaneously gluing the back side of the label. This is accomplished by applying a thin glue film to the pallet which is then pressed in intimate contact against the first label in the stack. After its removal, the label sticks on the entire glued area of the pallet until transferred to a “gripper” cylinder and removed from the pallet. The gripper cylinder then transfers the label to the container to be labeled. The various machine designs and techniques are well known within the labeling industry and to those skilled in the art. The “Krones Manual Of Labeling Technology” by Hermann Kronseder dated December 1978, is hereby incorporated by reference.
Attempts have been made to use polymeric substrates with high moisture vapor transmission rates (MVTR) such as films with micro perforations for drying of the water trapped between the label and the container and high solids tacky or pressure sensitive adhesive for good wet tack on conventional wet water based labeling equipment with little success. The high solids tacky adhesive required to stick to the polymeric substrate causes machining problems by gumming up the adhesive application system and creates cleanup issues. The high MVTR substrates also did not have good wet tack with existing commercially available adhesives that would machine without problems and did not dry rapidly enough making the labels prone to “swimming” or moving from the desired application area during down stream processing. The micro perforated materials allow adhesive to ooze thru the label contaminating the label surface ruining the graphics and making the label sticky. In addition, many of the current paper adhesives do not wet out and apply uniformly to non hydrophilic surfaces with the crude adhesive metering and application systems currently in use on existing paper labeling machinery. Without uniform application, wet out and wet tack, it will be impossible to successfully apply a polymeric label because of adhesive and application imperfections.
When plastic or glass containers are recycled, the first step involves cleaning, then label removal and separation of the labels from the used containers. When polymer labels are removed, they are sometimes difficult to separate from the liquid/label/container mixture that is formed during the recycling process if the density of the polymer label is high enough that it will not readily separate and float on the surface of the liquid that is used for label removal. The applicant has discovered that if the polymer stock for the label is a material having fine micro voids and a density that is substantially lower than the label removal fluid, not only will the labels be easily separated from the container/label/liquid mixture because they float on the surface of the label removal liquid which simplifies the recovery of the glass or plastic container for recycling, but the polymeric labels will also function well in wet glue PML labeling.
Accordingly, it is an object of the invention to provide a polymeric label particularly adapted for use in post mold wet applied labeling of polymeric and glass containers that would readily feed from the label magazine or gripper, adhere with sufficient tack without moving through post labeling handling and processing including but not limited to conveying, filling, case packing and palletizing and is adapted to recycling.
It is also an object of the invention to provide a polymeric label particularly adapted for use in post mold wet applied labeling of polymeric and glass containers that would have sufficient wet tack and affinity for water, a water based solution or adhesive used to allow for transfer of the wet water based adhesive to the polymeric label substrate from the applicator roll(s), pad(s) or pallet(s) of the labeling machine and is adapted to recycling.
It is also an object of the invention to provide a polymeric label for use in post mold wet applied labeling of polymeric and glass containers that would have a coefficient of expansion or contraction under the conditions which the container sees which is the same or compatible with that of the polymeric resin, glass or metal from which the container is made so that expansion and contraction of the container will not wrinkle or otherwise affect the integrity of the label and is adapted to recycling.
It is also an object of the invention to provide a polymeric label for use in wet applied post mold labeling which would combine suitable properties of modulus of elasticity and flexibility and would not be degraded by handling and flexing of the subsequent container and is adapted to recycling.